A known turbocharger supplies a turbocharged air to an engine by utilizing energy of an exhaust gas flowing into a turbine housing. In addition, an operating part such as a control valve for controlling the flow of the exhaust gas in the turbine housing is provided in the turbine housing so as to control the boost pressure of the air. Such the operating part is fixed to one end of a shaft extending to an outside through a bearing bore of a bearing provided on the turbine housing and driven from the outside via the shaft.
The temperature of the exhaust gas becomes high (over 800 degrees) and thus a gap is defined between the bearing bore and the shaft in the turbine housing for preventing the burning due to the thermal expansion, thermal deformation, and the like. At the same time, however, the exhaust gas may leak from this gap to the outside (atmosphere) from the turbine housing.
In order to solve the aforementioned drawback, JP08(1996)-334030A2 discloses an exhaust gas sealing system for a turbocharger. According to the disclosed system, a washer (sealing member) is disposed between an arm supporting the control valve and an end face of the bearing provided in the turbine housing so that the arm and the washer are pressed against the end face of the bearing by the pressure of the exhaust gas applied to the arm. At the same time, the washer and the shaft form no gap therebetween and then firmly become in contact with each other under the high temperature, thereby achieving the exhaust gas sealing system that may reduce the exhaust leaking from the gap between the bearing bore and the shaft. Further, JP05(1993)-248253A2 discloses another exhaust gas sealing system for a turbocharger. According to the disclosed system, a washer (sealing member) engaging with an inner diameter of the bearing bore of the turbine housing and a washer (sealing member) engaging with an outer diameter of the shaft are provided adjacent to each other in the axial direction. Then, a passage through which the exhaust gas leaks is brought to be elongated and bent as a labyrinth, thereby reducing the exhaust gas leaking through the gap formed between the bearing bore and the shaft.
According to the system disclosed in JP08(1996)-334030A2, the valve, the arm and the shaft vibrate in the axial direction due to the engine vibration when the engine is operated. Therefore, it may be difficult to press the arm and the washer against the end face of the bearing provided on the turbine housing by the pressure of the exhaust gas applied to the arm against inertia force generated by the vibration occurring in the valve, the arm and the shaft.
In addition, according to the system disclosed in JP05(1993)-248253A2, the arm vibrates in the axial direction by the engine vibration when the engine is operated. Therefore, gaps formed between the respective washers may vary in size or shape and thus it may be difficult to surely bring the passage for the exhaust gas like the labyrinth.
Further, According to aforementioned both disclosed systems, the shaft is inclined in the gap between the shaft and the bearing bore due to bias load applied when the control valve is operated. As a result, a gap is formed between the washer and the end face of the bearing, or between the washers, thereby preventing the sealing width or the gap between the washers from being uniformly retained. Furthermore, since the washer and the end face of the bearing, or the washers each other are slid each other when the shaft is rotated along with the operation of the control valve, thereby causing roughness of each surface. The sealing performance may be decreased accordingly.
Thus, a need exists for an exhaust gas sealing system for a turbocharger that can surely reduces the exhaust gas at a high temperature and a high pressure to be leaked from a gap formed between a bearing bore and a shaft in a turbine housing.